1. Field of the Invention
The present invention relates to an automatic offset compensating bipolar A/D converter circuit. More specifically, the invention relates to an A/D converter circuit which can delete offset error between a specific code of digital output and the analog voltage corresponding to the digital output.
2. Description of the Prior Art
A bipolar A/D converter has an input-output characteristic which is theoretically symmetrical about the origin. However, conventional bipolar A/D converters have a so-called offset error by which the input analog voltage is not 0 V when the digital output has zero value (0-------0). In order to eliminate the offset error, the MSB's or sign bits of binary codes expressed by 0 and 1, such as offset binary or 2' complement, are integrated to eliminate the offset error on the average in conventional bipolar A/D converters.
The aforementioned method is effective to compensate offset error which is caused by a comparator in a converter or by offset of reference voltage to approach zero. However, it is difficult to perfectly compensate 1/2LSB offset error, which is caused according to height of the quantizing step, to approach zero.